Method and device for the three-dimensional measurement of objects

ABSTRACT

Disclosed is a method for three-dimensionally measuring objects, according to which the positions of a measuring element ( 14 ) are determined by means of a locating method (e.g. optically, electromagnetically, or acoustically), said positions being relative to a reference system defined by the associated locating system ( 16 ), and desired dimensions of the object ( 24 ) are calculated from the determined positions of the measuring element. Also disclosed is a corresponding device for three-dimensionally measuring objects. The measuring element can be moved by means of a robot arm ( 26 ) or a flying object (.e.g. a type of zeppelin).

The invention relates to a method and to an apparatus for thethree-dimensional measurement of objects in accordance with the preambleof claim 1 and/or of claim 14.

In known methods for the three-dimensional measurement of objects suchas workpieces, the objects are positioned on a measuring table at whichan apparatus with a measuring element is movably arranged for thescanning of the outer contours of the objects, with the location of themeasuring element being able to be determined via linear,three-dimensional transducers in the x, y and z directions. As a rule,the measuring table is a ground, solid block of marble which is usuallyinstalled in a stationary manner.

The measuring element consists, for example, of a scanning measuringsphere which is mechanically connected to a force sensor to ensure acontinuous contact with the object. On scanning, the measuring sphere ismoved into contact with the object and along the object. A computerdetermines the outer dimensions of the three-dimensional object from themovement of the measuring sphere along the object using the lineartransducers which have a precisely fixed location to the measuringtable. Other apparatuses with pneumatic feelers, which can also bepositioned into the openings of the workpiece, are used for themeasurement of inner dimensions.

Such apparatuses for the three-dimensional measurement of objects arevery rarely used directly in production halls since, for example, wateror oil used there, chips which occur, vibrations which arise andelectrical problems can result in measuring imprecision. An additionaldisadvantage is the relatively low measuring speed due to the lineartransducers and the large space requirements due to the solid marblemeasuring tables.

Special measuring apparatuses are therefore often used in industry whichare only optimized for one measuring task, for example for a diametermeasurement of a piston. In addition to scanning spheres,electro-pneumatic transformers, capacitive sensors and inductivescanners are used as measuring elements. The workpieces are introducedinto the measuring apparatus using a handling system which can have avery complex design. A handling system is furthermore again required forthe removal of the workpieces from the measuring apparatus, for examplefor the classification into usable and non-usable workpieces orworkpieces which have to be reworked.

Measuring elements for the scanning of the object are provided, forexample, on a crane or a stand for large objects to be measured such ascar bodies. The crane or the stand and the object to be measured aremovable relative to one another in order to scan the object sectionallywith the measuring elements arranged on the crane or on the stand. It isdisadvantageous in this process that there is a limitation with respectto the size of the measurable object due to the dimensions of the standor to the range of the crane. The stand or the crane is moreover usuallyinstalled in a stationary manner and can therefore be transported to adifferent location for the measurement of objects with difficulty.

The measurement of larger objects and spaces therefore very oftenrequires a high effort. Since the measurement of large objects is apoint one as a rule, the actual shape of the objects is determined bymeasurement of a few points and interpolation or extrapolation for costreasons. This can result in substantial imprecision of the measureddata.

It is the object of the invention to provide an improved apparatus andan improved method for the three-dimensional measurement of objects withwhich the aforesaid disadvantages are at least very largely eliminated.

The object is satisfied by the features of the independent claims.

The object is in particular satisfied in that, in a method for thethree-dimensional measurement of objects in which a measuring element ismoved in space relative to an object to be measured, in particular alongits surface, the locations of the measuring element are determinedrelative to a reference system, in particular relative to a fixedreference system, and the dimensions of the object examined aredetermined from the locations of the measuring element determined, thelocations of the measuring element are determined by a locating methodwith reference to a reference system fixed by the associated locatingsystem and desired dimensions of the object are calculated from thelocations of the measuring element determined.

In accordance with the invention, it is therefore not linear transducerswhich are used, as previously, to determine the location of themeasuring element during the measurement, but a locating method withwhich the location of the measuring element can be sensed veryaccurately. The method for the three-dimensional measurement is alsoless prone to disturbances with respect to vibrations by the use of alocating method for the determination of the location of the measuringelement. It is therefore not necessary to use a solid, stationarymeasuring table and the method in accordance with the invention can alsobe used in an industrial environment, that is directly at the productionsite.

The method and the apparatus for the three-dimensional measurement ofobjects are moreover not limited to a maximum size of the objects to bemeasured, since a large spatial area can be measured with the help ofthe locating method. The apparatus for the three-dimensional measurementof objects can furthermore be transported relatively easily and cantherefore be used for a measurement of objects at different locations. Afast and precise measurement in three-dimensional space is above allmade possible since the movement of the measuring element is not limitedby the locating method as with linear transducers.

At least one physical field, in particular an acoustic, optical and/orelectromagnetic field, can be set up for the location of the measuringelement. This is done in particular by a plurality of transmitterspositioned around the measuring position as field sources of thephysical field, for example sources for visible and/or invisible light,whose locations fix the reference system for the locating method. Thedistance between the transmitters of the physical field and themeasuring element can be determined very precisely from the propagationspeed of the physical field from the signal transit time. The moretransmitters that are distributed in the space, the more precisely thelocation of the measuring element can be determined. This permits themeasurement of three-dimensional objects with an accuracy of up toapproximately ±1 μm.

In an embodiment, a unidirectional locating system can be used to locatethe measuring element, in particular in the manner of the globalpositioning system, GPS. It is consequently a method in which a one-waydistance measurement is carried out by means of the transit time of thesignals between the transmitters and corresponding sensors on or at themeasuring element. The measurement error is thereby kept small and,moreover, the calculation of the dimensions of the object from thedetermined locations of the measuring element is accelerated.

The measuring element can furthermore scan the object mechanically or ina contact-free manner. The former can, for example, be done using ascanning sphere which is rolled along the surface of the object to bemeasured. However, the scanning can also take place in a contact-freemanner, for example inductively, capacitively or using a pneumaticfeeler so that sensitive surfaces can also be measured. The determinedlocation of the measuring element is then corrected using theinductively, capacitively or pneumatically determined spacing of themeasuring element from the surface in order to determine the location ofthe measuring point on the surface. The scan takes place eithercontinuously or at individual scan points, with the current location ofthe measuring elements being determined and stored as a measured valueon every scan.

In a preferred embodiment, the measuring element can be moved by a robotarm. The measuring element can be fixedly installed at the robot arm;however, it can also be releasably secured to the robot arm and can inparticular be taken up by a grip of the robot arm as required. Forinstance, a customary industrial robot can be used for the measurementof the three-dimensional objects and can be combined with transmittersof a physical field and a measuring calculator to determine thedimensions of the three-dimensional object from the locations of themeasuring element determined via the locating system. Due to the use ofa locating system to determine the location of the measuring element,and thus also of the robot arm, the accuracy of the incremental encoderof the robot does not have to be very high, since the robot can also bevery accurately controlled with reference to the locations determined.For this reason, linear x, y, z transducers are also not required forthe control of the robot. Moreover, due to the use of a robot for themovement of the measuring element, more degrees of freedom of themovement of the measuring element can be realized in comparison with theprevious state of the art. Bore holes can, for example, also bemeasured.

The robot arm can moreover advantageously simultaneously be used for themovement of the object, in particular for the loading and/or unloadingof the measuring apparatus. An additional system for the locating andclassification of the workpieces thus becomes superfluous, for exampleon the measurement of workpieces.

In a further embodiment, the measuring element can be moved with aflying object. The flying object is maneuvered by cable or by remotecontrol; it can, for example, be a model helicopter. This also permitsthe measurement of large objects, with not only the outer surface ofobjects such as car bodies being able to be measured, but also, forexample, the inner surface of spaces.

Exchangeable measuring elements can furthermore be used. This permitsthe alternative or sequential use of different scanning methods, forexample using mechanical or inductive scanning elements. Moreover, ifthe measuring element is moved using a robot arm, an object to bemeasured can first be positioned by a grip of the robot arm andsubsequently be measured using an exchangeable measuring element takenup by the same grip or by a second grip.

The locating system can furthermore be calibrated via the transmittersand sensors by self-calibration. This permits a recalibration of thesystem carried out in short time intervals for which the measurementonly has to be interrupted for a short time.

The measuring element can moreover be supplied with energy in a wirelessmanner, in particular inductively or by means of an accumulator. Themeasurement data of the measuring element can moreover be transmitted ina wireless manner, in particular inductively or by radio. In both cases,the exchange of a measuring element is simplified and the measurementwith different measuring elements accelerated.

The object can be positioned at a zero position for the measurement.This simplifies the measurement, since the location of the measuringobject does not first have to be determined.

In a further embodiment, the object to be measured can be measured inaccordance with a grid, in particular with an asymmetrical grid. Themeasurement of the object can be accelerated by provision of a few gridpoints in specific regions to be measured with less accuracy.

Further advantageous embodiments of the invention are recited in thefollowing Figure description, in the drawings and in the dependentclaims.

The invention will be described in the following purely by way ofexample and with reference to the enclosed drawings. There are shown:

FIG. 1 a perspective view of a first embodiment of an apparatus inaccordance with the invention in a schematic representation;

FIG. 2 a perspective view of a second embodiment of an apparatus inaccordance with the invention likewise in a schematic representation.

FIRST EMBODIMENT

The first embodiment of the apparatus in accordance with the inventionshown in FIG. 1 comprises a measuring table 10, a robot 12, a measuringelement 14, a storage position 15 for different measuring elements, aplurality of transmitters 16 and a measuring and control computer 18.For the illustration of a measuring routine which can be used inproduction, a supply belt 20 and two take-away belts 22 and 23 forworkpieces 24 to be measured and already measured workpieces 24respectively are also shown in FIG. 1.

The transmitters 16 are arranged in the space and on the measuring tablesuch that they are distributed around the workpiece 24. The transmitters16 are, for example, transmitters for a radio signal, in particular aGPS signal.

The robot 12 is arranged at the measuring table 10 and has a grippingarm 26 whose free end holds the measuring element 14. The robot is acustomary industrial robot from its basic design and does not only takeup the measuring element 14 from the storage position 15 with thegripping arm 26, but also takes up the respective workpiece 24 to bemeasured from the supply belt 20 prior to the measurement, positions iton the measuring table 10 and puts the measured workpiece 24 down on thetake-away belt 22 or 23 after the measurement in dependence on whetherthe workpiece is in order or represents a reject.

The gripping arm 26 has a grip 30 at its free end with which themeasuring element 14 is taken up, a sensor not shown here for theelectromagnetic field generated by the transmitters 16 as well as aradio element which is likewise not shown here and which transmits thesignals of the transmitters 16 received by the sensor to a transmitterand receiver module 28 of the measuring and control computer 18.

The measuring element 14, for example, comprises an inductive scanner(not shown) for the scanning of the surface of the workpiece 24 and aradio element (likewise not shown) for the communication with thecontrol and measuring computer 18. Alternatively, the data of themeasuring element 14 can be transmitted inductively to a receiver in thegripping arm 26 and from this via electrical lines to the measuring andcontrol computer 18. The measuring element 14 is moreover supplied withenergy via the gripping arm 26 by means of an inductive coupling (notshown). The measuring element 14 is made exchangeable by this embodimentand can be taken up from the storage position 15 and immediately used ina suitably functional manner by the gripping arm 26 of the robot 12.

As mentioned above, the measuring and control computer 18 is fitted witha transmitter and receiver module 28. This transmitter and receivermodule 28 not only receives the signals of the transmitters 16, but alsoradios control signals to the transmitters 16, to the robot 12 and tothe measuring element 14. In addition, the transmitter and receivermodule 28 can receive the measured data of the measuring element 14 andof the sensor at the gripping arm 26.

To carry out the measurement, the first workpiece 24 to be measured onthe supply belt is gripped by the gripping arm 26 of the robot 12 andpositioned on the measuring table 10. The workpiece 24 is fixed there,for example attracted to the table by electromagnets. The gripping arm26 subsequently takes up the measuring element 14 from the storageposition 15 and scans the workpiece 24 with the measuring element 14. Onevery scan, the signals of the electromagnetic field generated by thetransmitters 16 and received by the sensor at the gripping arm 26 aretransmitted by the radio element present on the grip to the measuringand control computer 18.

The measuring and control computer 18 determines the transit times ofthe signals of the electromagnetic field between the transmitters 16 andthe sensor with reference to the signals of the sensor. The soughtdistances between the transmitters 16 and the sensor result from theproduct of the propagation speed of the electromagnetic field, which isknown, and of the transit time of the respective signal. The measuringand control computer 18 furthermore determines the current location ofthe sensor, and thus of the measuring element 14, from the computeddistances, while said measuring element scans the workpiece 24, andassigns these data to the respective measurement. The dimensions of theworkpiece 24 are determined from the detected locations of the measuringelement 14 and, with a contact-free scan, from the spacing of themeasuring element 14 from the workpiece 24.

The dimensions of the workpiece can be determined very accurately inthis manner, without a further device for the three-dimensionalmeasurement having to be used. The effort for a design of specialmeasuring apparatuses is dispensed with by the use of a conventionalmeasuring element 14 with an industrial robot 12 conventional in itsbasic design. It moreover makes it possible for the robot 12 to be ableto be used not only for the measurement, but also for the locating ofthe workpieces 24. This multiple use of the robot 12 is supported by theexchangeable design of the measuring elements 14.

The use of the described locating system in the three-dimensionalmeasurement of the workpieces 24 moreover permits a highly accuratecontrol of the gripping arm 26 and a determination of the workpiecedimensions using the determined locations of the sensor, without theclassical linear X, Y, Z transducers of conventional 3D measuringapparatuses having to be used. Moreover, no stabilizing block of marbleis also required as the measuring table for the highly accuratedetermination of the three-dimensional contour of the workpieces 24. Atthe same time, a measurement of three-dimensional objects with anaccuracy of up to ±1 μm is made possible due to the use of the locatingmethod for the location determination.

SECOND EMBODIMENT

A second embodiment of the apparatus in accordance with the inventionfor the three-dimensional measurement of objects is shown in FIG. 2.Components of this apparatus which coincide with components of the firstembodiment are provided with the same reference numerals.

The second embodiment comprises a flying object 50 made in the manner ofan airship, called a zeppelin in the following, a measuring element 52on a support 53, transmitters 16 and a measuring and control computer18.

The zeppelin 50 has lifting and control motors 54 to move the zeppelin50 in the space around an object 56 to be measured—shown as a closet inthe Figure. The lifting and control motors 54 are controlled via controlsignals which are transmitted to an antenna 58 of the zeppelin by thetransmitter and receiver module 28 of the measuring and controlcomputer. The measuring element 52 is provided on the front side of thezeppelin 50. The measured data of the measuring element 52 can betransmitted via the antenna 58 to the transmitter and receiver module 28of the measuring and control computer 18.

The zeppelin 50 furthermore carries at least one sensor (not shown inFIG. 2) for the reception of the signals of the electromagnetic fieldgenerated by the transmitters 16, in particular GPS signals. The sensorshave a defined position on or in the zeppelin with respect to themeasuring element 52 which can be determined with an elongate carrier 53of the measuring element 52 by means of a calculation of the spatialorientation of the carrier 53 relative to the sensors.

The energy supply of the zeppelin 50 is secured via high-energyaccumulators not shown in FIG. 1; however, a cable can also be providedfor the energy supply.

The measuring element 52 is made as a scanning sphere which is arrangedat the free end of the carrier 53 attached to the zeppelin. An inductivescanner can be provided as the carrier 53 for the fast recording of ameasuring path in the form of a jacket line of the closet 56. Themechanical contact with the object is thus secured and the frictionbetween the scanning sphere and the object is reduced.

In operation, the zeppelin 50 is moved in the space around the closet 56to be measured by radio by the measuring and control computer 18 suchthat the scanning sphere of the measuring element 52 comes into contactwith the surface of the closet 56 to be measured. To be able to scanlarger objects fast and accurately, the space is divided into a gridstored in the measuring and control computer. The grid can beasymmetrical to be able to steer to a large number of points with thezeppelin 50 at specific locations of the space or to be able to scanthem with the measuring element 52.

Once the measuring element 52 has come into contact with the closet 56,the zeppelin 50 is moved along the cabinet, while the scanning sphere ofthe measuring element 52 remains in contact with the surface of thecabinet 56, to determine desired dimensions of the closet 56. For thispurpose, as in the first embodiment, a distance measurement is carriedout between the transmitters 16 and the sensors and the location of thezeppelin, and thus the location of the measuring element 52, isdetermined from the detected distance values. The signals of thetransmitters 16 received by the sensors are transmitted for this purposeto the measuring and control computer 18 by radio via the antenna 58. Atthe same time, the measuring and control computer 18 checks whether thescanning sphere is in contact with the closet. The dimensions of thecloset 56 to be determined are computed from the detected locations ofthe measuring element 52 and, with contact-free measurement, from thespacing of the measuring element 52 from the surface.

The second embodiment is therefore a kind of flying probe forthree-dimensional measurement and permits not only the three-dimensionalmeasurement of large objects, but also the measurement of inner spacesdue to the large range of the zeppelin 50.

For this purpose, light sources or sound sources, for example ultrasonicsources, can also be used alone or can be combined with one another. Thesensors on the zeppelin 50 can then include optical or acousticinterferometers which determine phase shifts with which the locations ofthe measuring element, and thus the dimensions of large objects or thedimensions of inner spaces, can be determined even more accurately.

The sensors for the field cannot only be arranged at the grip or on theflying object, but alternatively or additionally at or in the measuringelement, if sufficient space is present there, or also at a carrier ofthe measuring element. Internal, field-independent sensors can moreoverbe provided to determine the orientation of the measuring elements inthe space, in particular relative to the grip.

The measuring system in accordance with the invention can advantageouslyalso be used under water, for example in nuclear power stations.

REFERENCE NUMERAL LIST

-   10 measuring table-   12 robot-   14 measuring element-   15 measuring element storage position-   16 transmitter-   18 measuring and control computer-   20 supply belt-   22, 23 take-away belt-   24 workpiece-   26 gripping arm-   28 transmitter and receiver module-   30 grip-   50 zeppelin-   52 measuring element-   53 carrier-   54 lifting and control motor-   56 object-   58 antenna

1.-25. (canceled)
 26. A method for the three-dimensional measurement ofobjects in which a measuring element (14; 52) is moved in space relativeto an object to be measured, in particular along its surface, thelocations of the measuring element (14; 52) are determined relative to areference system, in particular relative to a fixed reference system,and the dimensions of the object (24; 56) examined are determined fromthe detected locations of the measuring element (14; 52), characterizedin that the locations of the measuring element (14; 52) are determinedby a locating method with reference to a reference system fixed by theassociated locating system (16) and desired dimensions of the object(24; 56) are calculated from the locations of the measuring element (14;52) determined in this manner.
 27. A method in accordance with claim 26,characterized in that at least one physical field, in particular anacoustic, optical and/or electromagnetic field, can be set up for thelocation of the measuring element (14; 52).
 28. A method in accordancewith claim 26, characterized in that a unidirectional locating system(16), in particular in the manner of the so-called global positioningsystem, GPS, is used for the locating of the measuring element (14; 52).29. A method in accordance with claim 26, characterized in that themeasuring element (14; 52) scans the object (24; 56) mechanically or ina contact-free manner.
 30. A method in accordance with claim 26,characterized in that the measuring element (14; 52) is moved by therobot arm (26).
 31. A method in accordance with claim 26, characterizedin that the robot arm (26) is simultaneously used for the movement ofthe object, in particular for the loading and/or unloading of themeasuring apparatus.
 32. A method in accordance with claim 26,characterized in that the measuring element (14; 52) is moved by aflying object (50).
 33. A method in accordance with claim 26,characterized in that at least one exchangeable measuring element (14;52) is used.
 34. A method in accordance with claim 26, characterized inthat the locating system (16) is calibrated by self-calibration.
 35. Amethod in accordance with claim 26, characterized in that the measuringelement (14; 52) is supplied with energy in a wireless manner, inparticular inductively or by means of an accumulator.
 36. A method inaccordance with claim 26, characterized in that the measurement data ofthe measuring element (14; 52) are transmitted in a wireless manner, inparticular inductively or by radio.
 37. An apparatus in accordance withclaim 26 characterized in that the object (24; 56) is positioned at azero position for the measurement.
 38. An apparatus in accordance withclaim 26, characterized in that the object (24; 56) to be measured ismeasured in accordance with a grid, in particular with an asymmetricalgrid.
 39. An apparatus for the three-dimensional measurement of objectscomprising a measured element (14; 52) movable in space relative to anobject to be measured, in particular along its surface; means for thedetermination of the location of the measuring element (14; 52) at themeasuring positions relative to a reference system, in particularrelative to a fixed reference system, and means for the determination ofthe dimensions of the object (24; 56) from the detected locations of themeasuring element (14; 52), characterized in that a locating system (16)is provided for the determination of the location of the measuringelement (14; 52) with reference to the reference system fixed by thelocating system (16) and in that means (18) are provided for thecalculation of object dimensions from the locations determined in thismanner.
 40. An apparatus in accordance with claim 39, characterized inthat the locating system (16) has at least one means (16) for thesetting up of a physical field, in particular of an acoustic, opticaland/or electromagnetic field.
 41. An apparatus in accordance with claim39, characterized in that the locating system (16) is made as aunidirectional locating system (16), in particular in the manner of theso-called global positioning system, GPS.
 42. An apparatus in accordancewith claim 39, characterized in that the measuring element (14; 52) ismade as a mechanical or contact-free scanning element.
 43. An apparatusin accordance with claim 39, characterized in that the measuring element(14; 52) is arranged at a robot arm (26).
 44. An apparatus in accordancewith claim 43, characterized in that the robot arm (26) has a grippingelement (30) for the gripping of the measuring element (14; 52) and/orof the object (24; 56) and is made to move the measuring element (14;52) between pick-up and put-down positions and the measuring position.45. An apparatus in accordance with claim 39, characterized in that themeasuring element (14; 52) is arranged at a flying object (50).
 46. Anapparatus in accordance with claim 39, characterized in that themeasuring element (14; 52) is exchangeable.
 47. An apparatus inaccordance with claim 39, characterized in that means are provided forthe self-calibration of the locating system.
 48. An apparatus inaccordance with claim 39, characterized in that means (28) are providedfor the wireless energy supply of the measuring element (14; 52), inparticular means for the inductive energy supply or an accumulator. 49.An apparatus in accordance with claim 39, characterized in that meansare provided for the wireless transmission of the measured data, inparticular means for inductive transmission or for transmission byradio.
 50. An apparatus in accordance with claim 39, characterized inthat a zero position is provided for the object (24; 56) to be measured.